An autofocus optical system uses a sensor, a control system, and a motor to focus fully automatically or manually on a selected point or area. Cameras and other image capturing devices have used built-in autofocus systems for many years, and yet many photographers still struggle with the accuracy and repeatability of these systems.
Autofocus is a great convenience, especially in fast shooting situations; however, autofocus error still causes many images to be improperly focused. Photographers tend to blame the improper focus on the camera choosing the wrong object (or the wrong point on the object) as the focal point. However, another possibility is that the autofocus feature is simply not functioning properly. In such cases, the photographer may have to return the lens and/or camera body back to the manufacturer for recalibration or replacement. This option can be both time consuming and expensive.